1. Field of the Invention
This invention relates to improvements in rotary drive apparatuses and, more particularly, to improvements in rotary drive apparatuses in which an endless or a continuous cable is connected to both a driving member and a driven member.
2. Relevant Background
U.S. Pat. No. 4,351,197 (Carson) discloses a rotary drive apparatus in which a driving member or element, a screw, is coupled by a cable to a driven element, a drum. The screw is in turn coupled to an electric motor. Rotation of the screw results in rotation of the drum. The cable is terminated at both ends on the drum, and is arranged between the drum and the screw to transmit the driving force of the rotating screw to the drum. More particularly, the cable is connected at one end to the drum by a tensioning device. The cable is then threaded back and forth a number of times between grooves in the outside cylindrical wall of the drum and corresponding helical grooves in the outside cylindrical wall of the screw. The cable is then connected again at its terminating end to the drum. There may be a substantial difference in the diameters of the drum and the screw to enable a single rotation of the screw to produce a relatively small angular movement of the drum. This relationship allows a load on the driven member to be positioned with substantial accuracy or precision.
U.S. Pat. No. 4,757,723 (Carson) discloses a rotary drive apparatus in which a cable is coupled between a driving member and a driven member with both ends of the cable terminated in the driven member. Both ends of the cable, which couples the two members together, are connected to springs, which maintain a tension on the cable.
U.S. Pat. No. 4,787,259 (Carson) discloses a rotary drive system in which a single driven member is coupled to a plurality of driving members. One end of the cable is terminated in a spring to maintain tension on the cable. The other end of the cable is disclosed as being hard terminated, or fixed within the driven member.
U.S. Pat. No. 4,796,478 (Carson) discloses a rotary drive apparatus designed to provide nonlinear rotation by using a pivoting arm secured to the driving member and a driven member having an axis of rotation offset from its geometric center. A pair of cables is illustratively used in the apparatus, with the ends of the cables being terminated in the driven member.
U.S. Pat. No. 5,105,672 (Carson et al.) discloses a rotary drive apparatus in which one of two rotating members, either the driving member or the driven member, includes a smooth outer surface. Multiple cables are shown, with the cables being terminated on the driven member.
Since each of the above apparatuses disclose a cable connection in which the ends of the drive cables are terminated in the driven member, there is a limited rotational ability of the driven member. The rotational ability can exceed one or two revolutions but cannot be continuous. There are times when a driven member needs to be rotated many revolutions, or continuously. Accordingly, there is a need for an endless or essentially continuous cable connection between a driving member and the driven member.
It will be noted that at least one end of the cables disclosed in some of the above noted patents are spring terminated to provide tension on the cables. A spring termination directly on the end of each cable is, of course, not possible with an endless cable. Accordingly, different tensioning elements are required for a rotary drive cable system when an endless or essentially continuous cable is being used.